Aviation lubricating oil



Patented May 8,

avm'riou Lnnnrcarmc on.

No Drawing. Application September 1 .5, 19413,

Serial No. 502,106

15 Claims. (c1. 252-23) This invention relates to addition agents whichcontribute valuable properties to lubricating oil. It also relates toimproved lubricating compositionscontaining the herein describedadditives.

It is known that a substantially non-corrosive, undoped, lubricating oilgenerally'becomes progressively corrosive under ordinary conditions ofengine use. This tendency is increased or accelerated. for instance, byan elevation of temperature, by traces of dissolved copper, bydegradation products formed in the oil, and by other factors. It is acommon practice to add a detergent to a lubricating oil in order toassist in the removal of soot or sludge which is formed in the engineoperation and thus to help keep the bearing surfaces clear. However,normally such detergents simultaneously contribute to or increase thecorrosiveness of the lubricating oil. Similarly, additives employed forother purposes may, also prove corrosive. This result is particularlyunfortunate, if uncorrected, when ittions may preferentially remove thecopper.-

Again, the effect at high temperatures modern bearings, of sulfurderived from certain of its compounds or even found free in the oil orfuel, may be very serious. Thus, in hot countries a crankcasetemperature of 250-300 F. may

occur, with the corresponding bearing temperatures going up to 325 F. or350 F. Under these conditions sulfur can produce hard, brittle, blackdeposits on copper-lead or silver bearings. Such deposits may adhere andreduce the bearing clearance or they may break up and gouge out thebearing, in either event resulting in bear-- ing failure.

The problem 'of engine deposits is particularly acute in aviatio andsimilar engines, in which the high temperatures developed in thecylinders tend to act upon lubricating oils to cause the deposition ofresinous and varnish-like products on the pistons and elsewhere and toproduce lacquer-like coatings and carbonaceous materials, which in timetend to cause ring and valve sticking and interfere with engineoperation. High piston temperatures found especially in aviation enginepromote t formation of deposits which, in turn, aggravate the situationby reducing the heat transfer. Furthermore, fuel residues fromincomplete combustion of fuel contribute to the deposition oflacquer-like and carbonaceous materials in the engine. Solution of theproblem is additionally complicated by rigid government specificationsfor aviation lubricating oil which restrict the incorporation of anyadditives, such as metallic salts, which would leave a non-volatile ashupon combustion. At the most, thetotal ash content should not exceedabout 0.2% (determined as sulfate).

Accordingly, it is an object of this invention to provide lubricatingoil compositions which have improved properties in one or more of thefollowing qualities: high temperature detergency, decreased piston ringsticking, wear reduction, corrosion resistance; stability in presence ofcopper or crankcase catalyst, oxidation stability, and the like. Anotherpurpose is to produce a superior heavy duty lubricant particularly suitable for use in aircraft and other internal combustion engines operatingat relatively high cylinder temperatures. Other objects will be apparentfrom the following description.

It has now been found that such lubricating problems may be overcome toa notable extent by the incorporation in a lubricating oil of twoadditives. The first of these additives is an oil-miscible metal salt ofthe condensation product of a low molecular weight aldehyde with ahydrocarbon substituted phenol. The second additive is an organicsulfur-containing antioxidant (as will be more fully describedhereinafter).

The first additive is more fully described by the following. It isinitially a condensation product of a phenol with an aldehyde. Thephenol must have an available ortho position, i. e. an unsubstituted p'ition ortho to the hydroxyl radical, and also such substituent groups,preferably in the 4 or 2,4 positions, as will promote oil solubility.For example, alkyl, cycloalkyl or aryl groups, such as butyl, amyl,hexyl, heptyl, octyl, nonyl, decyl, lauryl, stearyl, oleyl, cyclohexyl,methylcyclohexyl, ethylcyclohexyl, dimethylcyclohexyl, propylcyclohexyl,trimethylcyclohexyl, dicyclohexyl, methylated dicyclohexyl, benzyl,ethylphenyl, etc., are effective. The aromatic nucleus as well asattached hydrocarbon radicals may also contain chlorine. The aromaticnucleus may be monoor di-cyclic, resulting in such nuclei asnaphthalene, tetraline, diphenyl, etc.

A. lower molecular weight aldehyde, preferably formaldehyde oracetaldehyde, iscondensed with the phenol at the ortho position by waysknown to the art, for example by heating with acid or basic catalyst,whereby a resinous condensation product is obtained. Depending uponstarting materials and condensation conditions, the products vary inappearance from viscous liquids to more or less brittle solids which mayor may not be crystallized. A number of such resinous condensationproducts are commercially available, and since their methods ofmanufacture are generally known, further details regarding suchmanufacture will not be recounted here.

The phenolic resin is in turn converted to the metallic salt, forexample by heating with hydrated lime to produce the calcium salt. Ingeneral, the alkaline earth metals are preferred to form the salt,although other polyvalent metals such as Cu, Zn, Al, Pb, Fe, Ni, Co, Mn,Cr and Sn may be employed.

The resultant metal phenates may be difiicultly soluble, in oil.However, they may be incorporated in oil by the procedure described byCorthen be diluted with further oil'to give the desired saltconcentration when needed. On the other hand, the salt may often beincorporated in alubricating oil, without preparing an intermediateconcentrate, by simply adding the desired concentration of the salt tothe oil at an elevated temperature with agitation.

- The amounts of the phenol-aldehyde resin salt which may be added toaviation and similar high temperature lubricating oils must not exceedabout 0.2% ash, because ash in these lubricating oils eventuallyaccumulates in the combustion chamber of the aviation engine by leakingpast the piston and piston rings, or else leaking into the super-charger(with which most aviation engines are now equipped) whence it returnswith the air to the combustion chamber. About of the oil lost inaviation engines is normally by way of the super-charger.

It has been stated that phenol-aldehyde resin salts act as anti-oxidants"in lubricating oils. However, we found that under the high temperatureconditions in aviation engines and in the amounts of ash contents of0.2% or less, such is not the case. Only when added in much largeramounts, 1. e. of ash contents of 0.3% or higher, do these salts showanti-oxidant properties in aviation lubricants under aviationlubricating, conditions.

As a result of their lack of anti-oxidant properties, aviationlubricating oils containing these salts in the perimissible amounts arenot only oxidation unstable, but may also be corrosive, and to overcomethese detrimental efiects. we add a second addition agent to lubricatingoil as described below.

The second additive is an oil-soluble, relatively stable, organic sulfurantioxidant, free from corrosive sulfur, having preferably not more thana single polar radical (if any) other than a sulfur containing radical.Sulfurantioxidants should contain at least about 7 carbon atoms, andpreferably 10 or more, and are characterized by containing the sulfur,in a form so that it is somewhat reactive, but not too reactive, withheavy metals such as copper, lead, iron, etc., at temperatures between,say, C. and 300 C.

.It is known that sulfur in the form of sulfides (RSR', where R and Rare the same or different hydrocarbon radicals), thiophanes, thiophenes,sulfoxides, sulfones, sulfonates, etc., is too inert for antioxidantpurposes. Antioxidant sulfur may be in the form of mercaptans, as indecyl mercaptans, dodecyl mercaptans, cetyi mercaptans, oleylmercaptans, stearyl mercantans, butyl or other higher alkyl thiophenes,thionaphthols, alkyl thionaphthols, etc.; or of disulfides (RSSR, as indiamyl disulfide and higher dialkyl disulfides, e. g. wax disulfides,diphenyl disulfides, dibenzyl disulfide, dinaphthyl disulfides, etc); orof sulfur compounds formed by attaching sulfur to an olefinic doublebond (as by reacting sulfur with olefins at temperatures of about 150 C.to 300 C.) which compounds are believed to contain the structure (sulfurin epithio linkage).

Many sulfur compounds naturally occurring in petroleum oils are usefulantioxidants, provided they have the necessary reactivity. These haveseen described in detail in the copending appliaction being restrictedin most instances to lower :ation, Serial No. 496,678, filed July 28,1943, by

iistillates with clay or other refining agents, or

n the polymerization of normally gaseous olefins ;o produce gasoline orthe like (e. g. sulfurized nethyl pentadiene polymer); sulfurized estersof msaturated fatty acids with monohydrie alco- 1o1s, as methyl, ethyl,propyl, etc., oleate, or inoleate; sulfurized sperm oil; sulfurizedjojoba )il; etc. Less desirable are vsulfurized fatty oils vhich containthree ester radicals and hence tend cause excessive carbon formationunder the iigh temperature conditions of aviation engines Higherpolysulfides, such as compounds of the ;ype RSnR' where n is a wholenumber of 3 or iigher, as -well as other sulfur compounds con- .ainingcorrosive sulfur, are so reactive that they tttack bearing metals,causing a build-up of a .hick sulfide film which eventually breaks off,eaving behind a severely damaged bearing surace.

Effective amounts of the sulfur containing addiives in an aviationlubricating oil are in the order if 0.025% to 0.30% by weight of addedsulfur, a1: hough quantities of between 0.05% and 0.1% are lsuallysufllcient. Amounts of the metallic |henate between about 0.4% and 0.2%sulfate ash nay be'employed. It will be seen that the small .mounts ofadditives suflicient to accomplish the iresent purpose are much lessthan would be re- [uired to alter the viscosity omposition.

It has been found that the combination of the .ldehyde-phenol condensatemetal salt and a sulur antioxidant in aviation lubricating oil has ad-'antages which could not be obtained by any ther combination ofadditives. These advanages are, in particular, non-corrosiveness,deterency at high operating temperatures (with reulting enginecleanliness and prevention of ring ticking), prevention-or at leastreduction-of lard carbon formation and a hitherto unachieved eduction inwear, especially of piston rings.

To appreciate these advantages, it may be well 0 consider a few of thedifliculties which confront he producer of improved aviation lubricants.It

of the lubricatingwell known that ring sticking is one of themost Irequent causes of damage to aviation engines hich are lubricated bystraight mineral lubriating oils. While ring sticking can be overcome aa certain extent by the use of tapered piston ings, this advantage isgained at the expense f .a. new difliculty, namely, ring feathering.Ring ticking in aviation engines is a high tempera- .ll'e detergencyproblem, while ring'feathering L a wear problem.

Many detergents have been proposed to overome ring sticking. However,with few excepons they fail to function at the high temperan'es ofaviation engine operation, their beneficial temperatures such as occurin Diesel engines and automotive engines. It has been discovered,however, that the aldehyde-phenol condensate salts of this inventionexert an unexpected detergency at high temperatures, but not at lowtemperatures. At the same time, these salts somewhat reduce engine wearand also cause a very pronounced softening of hard carbon normallyformed.

Now as a result of the presence of a metal containing detergent,corrosiveness of the oil increases. It has been said that antioxidantsovercome corrosiveness induced by detergents. ever, this does not alwaysappear to be true. For example, the aldehyde-phenol condensate salts areknown to exhibit antioxidant action at low temperature and thereforemight be expected to inhibit this corrosiveness. However, this was foundnot to be the case when employing 0.2% (sulfate ash) of the additive.Certain other antioxidants, like secondary aromatic amines, e. g.diphenylamine, etc., do to some extent in hibitthis corrosiveness, buthave the disadvantage of causing at least a partial'loss of the carbonsoftening properties. Moreover, these inhibitors, like the ordinaryphenolic inhibitors, such as the 2,6-di-tertiary-butyl-4-methyl-phenol,or the amino phenols as para-benzylaminophenol, fail to have any effecton the wear properties.

The sulfurized antioxidants described earlier, however, have a very.peculiar effect on the aviation oil in combination with thealdehyde-phenol condensate salt. Not only d they do away with thecorrosiveness of the oil, but they further greatly enhance the wearreduction and in some instances furtherreduce hard carbon formation. Theadditive effect in the matter of wear reduc tion in itself is believedto be unusual. As a rule, two wear reducing agents do not cooperateunless they meet certain conditions indicated below, and

on the contrary merely compete for the surface,.

the more strongly absorbed compound displacing the other. Therefore, inso far as wear reduction The mechanism of boundary lubrication,Proceedings of 71118 Royal Society of London, Serial A,,No. 968, vol.177, pp. 90 to 118, December, 1940, and in the Proceedings of theSpecial Summer Conference on Friction and Surface Finish ofMassachusetts Institute of Technology, Cambridge, Mass., June 5, 6 and'7, 1940, p. 112, has it been known that two or more wear reducingagents cooperate. However neither of the two additives of this inventionis a chemical polishing agent, although some of the sulfur antioxidantsmay fall into the class of wedging compounds.

Due to" this strong wear reducing effect combined with the detergency,the present oil will ameliorate high temperaturedifiiculties whetherdueto ring sticking-or ring feathering, so that it may be employedadvantageously with either the straight or tapered type of piston ring.

' In military aircraft engine service in which piston ring beltlubrication is a primary problem,

, this lubricating oil composition, by its reduction of ring stickingand wear, offers a unique and- The preparation of a typicalaldehyde-phenol condensate salt is illustrated by reference to the useof calcium salts of methylene bis p-isooctylphenol. This compound wasprepared by condensing phenol and di-isobutylene to yield an(principally para) isooctylphenol. This was then condensed withformaldehyde to yield the resinous condensation product containing aboutfive molecules of isooctylphenol per molecule of resin, .1

but which for convenience is called methylene bis p-isooctylphenol. Thecondensate was converted to calcium salt by reaction with lime asfollows: About equal weights of resin and CaO were ground together to afine powder. Water was added and the mixture heated on a steam bath inan open vessel. A vigorous reaction took place involving hydration ofCaO and formation of the phenate salt. benzene and filtered from. excessCa(OI-I) 2. The bulk of the benzene was removed by distillation atatmospheric pressure; the remainder of the solvent was stripped underreduced pressure.

The resulting residue, a glassy amorphous solid, was then ground to ayellow-green powder. The

sulfate ash values of different batches varied from about 20% to 22%.

Our aviation oil additives were tested alone and together in themultiple four-ball machine similar in principle to th Boerlage apparatusdescribed in the magazine, Engineering, volume 136, July 14, 1933. Thisapparatus comprises four steel balls arranged in pyramid formation. Thetop ball is rotated by spindles against the three bottom ballswhich areclamped in a stationary ball holder. The balls are immersed in the oilto be tested. Tests were run for two hours at 700 R. P. M. under variousloads and at a controlled temperature of 130 C. The diameters of the Thesalt was taken up in warm Results were as follows:

TABLE I WEAR EVALUATION IN THE MULTIPLE FOUR-BALL MACHINE [A refined,undopcd, commercial aviation lubricating oil, -125 S. U. at 210 F. wasemployed] Scar diameter (mm.) at the No. of following Additivedeterloads, kg.

minations 1 None 4 .29 .70 .75 2 Calcium salt of methylene bisp-isooctylphenol (sulfate ash=0.l%) 2 l2 35 73 3 Calcium salt ofmethylene bis p-isooctylphenol (sulfate ash=0.3)%) 2 l1 l9 24 4 Calciumsalt of methylene bis p-isooctylphenol+barium dialkyl dithiophosphate :1ratio, total sulfate ash=0.1%) 2 14 47 77 5 Calcium salt. of methylenebis p-isooctylphenol+calcium petroleum sulionate (4:1 ratio, totalsulfate ash=0.l%) 2 l1 34 73 6 Calcium salt of methylene bisp-isooctylphenol+suliurized wax olefin (sulfate ash=0. 1%, added sulfur=0.1%) 2 .13 .21 .28 7 Barium dialkyl dithiophosphate (B280. ash=0.22%) 224 .30 .34

The doped and undoped oils were then further tested by a test known asthe thrustbearing corrosion test (described in the National PetroleumNews, September 17, 1941, pp. 12294-296) which is carried out asfollows: A hardened steel disc is made to rotate for 20 hours underconstant pressure against three flat copper-lead bearings. The bearingassembly rests in a steel cup filled with the oil to be tested, and thetemperature of the oil is maintained at a predetermined figure bythermostatic control. The bearings are weighed before and after thetest, the difference in weight representing the loss sustained durin thetest.

TABLE II 'Ins'rs IN Tr-musr BEARING CORROSION MACHINE [Fixed conditions:Cu-Pb bearings,

20 hours duration, p. s. i. Thrust, 2400 R. I. M. A

refined, undoped, commercial aviation lubricating oil, 115-125 S. U. at210 F. was employed] Bearing weight loss in Estimated Additive appro rimate (Delta s=0.1% for each additive) ggggg 0. o. c. c. o. empm 0'. None.I I. 0. l 0. 3 26. 8 180. Calcium salt of methylene bisp-isooctylphenol (sulfate 0.3 0. 7 49. 0 47. 7 155' &Sh=0-1%) 0.1 0.617.8 v o. 2+sulfurized wax olefin 0.3 g. g 0. 3 --0. 4 Above 160. N0.2+sulfurized sperm oil 0.6 01 2 o. 1 Above 110. No. 2-1-dibenzyldisulfide 0. 8 4. 8 31. 4 155. No. 2+dodeeyl disulfide 0. 0 7. 5 29. 8Below l5 -L No. 2+suli'urized methyl pentadiene polym 8.8 0. 5 0.1 Above170.

wear scars worn on the three balls forming the base of the pyramid werethen measured, and the average taken as the true indication of wear.

The oxidation stability of lubricating oil containing the presentadditives was also determined in the presence of copper and crankcasecatalysts as follows:

TABLE III STABILITY AND Snuncme DETERMINATIONS I [A refined, undoped,commercial aviation lubricating oil, 115-125 S. U. at 210 F. wasemployed. Temperature, 150 C nk Catalyst: 1 cm. Cu./g. oil O Addmws 18001 N t a] s h 1 U m eu r apom casopenoxygen 0. tion No. tanc gg 1800 gtime increase increase insoluble Hours Per cent Per cent Hours one 9. 43. 7 1B. 5 0. 04 @1- f 2Calciumsaltoimethylenebisp-isooctylpbenol(sulfate ash =0.1%) 8. s 4. 016.0 t 3 Preoeding+sulfurized wax olefin (added su1fur=0.1%) 65. 4 3. 217. 6 o

' All oxidation products corrected to 1800 ml. oxygen absorbed/100 oil,assuming amount of product is proportional to oxygen absorbed.

t Sediment centrifuged from used oil drained from auto craukcasw {see 35Ind. Eng. Chem. 681 (1943)).

3 Oxidation curve shows induction period.

Efiectiveness of a lubricant containing the presnt combination oflubricating oil additives in ctual engine tests as well as comparisonwith nine other blends may be seen from the follow- Ilg data: T IVtrmnme CORROSIVENESS AND USED OIL PROPERTIES Lawson 1 cylinder liquidcooled engine peed 1700 R.P.M.

MEP 55 psi.

. 1.6 H.P. 1 kw.)

Aviation base-stock 40 hours [A refined, undoped, commercial aviationlubricating oil, 115-125 S. U. at 210 F. was employed] Cu-Pb Sap. No.Neut. Concentration bearing 01] con- MgKOH MgKOH Isopent. Chlor.Additive in percent weight sumption, ins.,

sulfate ash loss, cc./hr. percent percent mg./cm. g g

0119 1.3 21.1 0.8 0.01 0.01 aicium salt of methylene bisp-isooctylphenol 8; alcium salt ofmethylene bis p-is00ctylphenol+sul-0.10:1: .1. 1:0 313 416 014 0.06 0:08 turized wax olefin. 0.1017? w.added- 0.9 4.9 4.3 0.4 0. 05 0. 04

su ur.

TABLE V Prsron RING WEAR CFR 1 cyl. variable comp. ratio Diesel- 8 ed900 R, P. M. B EP 60p. s. i. Air intake temp 50 C. refined, undoped,commercial aviation lubricating oil, 115-125 S. U. at 210 F. wasemployed] Tenpera- 'Iiotal ures p s on Additive Test ring Per cent.

length weight wear I Jacket Oil loss 5 Hours C. 0. G'mme callciumbsaltti)! metltiy ene 18 psoocty phenol (sulfate ash= 40 0.1%) 52 60 93 0.0845 70 7 Calcium salt of methylene bis p-isooctylphenol+sulfurized waxolefin (added sulfur=0.1%) 52 60 93 0.0662 1 49 1 Per cent wear= totalpiston ring weight loss ressed as er cent that with undoped oil. exp p 1Average.

TABLE VI GENERAL PERFORMANCE Pnopna'rras Speed 2350 R. P M IME 225 p. s1 Cylinder temperature:

Head F. Base" 325 F. Fuel 100 octane No. aviation fuel L refined,undoped, commercial aviation lubricating oil, 115-125 S. U. at 210 F.was employed] Additives Result None A 1 B 1 30 est length, hours--- 2050 50 acquer rating 49 17 7 istqn ring weight loss, gm. 5.95 0.29 0.11eating weight loss, rug/cm. 0.14 0.18 0.18 sed oil properties:

Saponiiicetion No., 'f 1.7 3.5 2 5 Neutralization No., M 10.2 0.8 0.8Iso entane insolubles, per cent w. .47 L2 C orolorm insolubles, per centw. .18 -1 Viscosity (cs.) at- 1 Additive A=calcium salt of methylene bisp-isooctylphenol,

1% sulfate ash, sulfurized wax olefin, added sulfur or delta S=0.l%.

|additive B =additive A+0.05% sulfate ash of calcium petroleum one o.

Norm-Test is normally 50 hours in length. Undoped oils fail at lortertimes due to severe wear of piston rings resulting in excessive low-byand oil consumption.

bases as primary, secondary, tertiary and quaternary amines.

Examples of detergent; forming acids are the various fatty acids of,say, 10 to 30 carbon atoms,

wool fat acids, parafiin wax acids (produced by oxidation of parafl'inwax), chlorinated fatty acids, rosin acids, aromatic carboxylic acidsincluding aromatic'fatty acids, aromatic hydroxy fatty acids, parafiinwax benzoic acids, various alkyl salicylic acids, phthalic acidmono-esters, aromatic keto acids, aromatic" ether acids; diphenols asdi-(alkylphenel) sulfides and disulfides, methylenebis alkylphenols;sulfonic acids such as may be produced by .treatment of alkyl arylhydrocarbons or high boiling petroleum oils with sulfuric acid; sulfuricacid mono-esters; phosphoric, arsenic and antimony acid monoand(ii-esters, including the corresponding thio phosphoric, arsenic andantimony acids; phosphonic and arsonic acids, etc.

Additional detergents are the alkaline earth phosphate di-esters,including the thiophosphate di-esters; the alkaline earth diphenolates,specifically the calcium and barium salts of diphenol 0 mono and polysulfides.

Non-metallic detergents include compounds such as the phosphatides (e.g. lecithin), certain fatty oils as rapeseed oils, voltolized fatty ormineral oils, etc.

An excellent metallic detergent for the present purpose is the calciumsalt of oil soluble petroleum sulfonic acids. This may be presentadvantageously in the amount of about 0.025% to 0.2% sulfate ash.

Antioxidants comprise several types, for example alkyl phenols such as2,4,6-trimethylphenol, pentamethylphenol,2,4-dimethyl-6-tertiarybutylphenol, 2,4-dimethyl-6-octylphenol,2,6-di-tertiary-butyl-4-methylphenol, 2,4,6 tritertiary-butylphenol,etc.; amino phenols as benzyl amino phenols; amines such as dibutyl'containing a minimum of carbon atoms.

We claim as our invention:

1. A low ash content lubricating oil for high temperature internalcombustion engines containing an oil-miscible metal salt of thecondensation product of an aldehyde and an arcmatic hydroxy compound inamount sufiicient to give high temperature detergent action, but notexceeding about 0.2%, based on sulfate ash, and an oxidation-inhibitingquantity of an oilsoluble, sulfur-containing, organic compoundpossessing antioxidant, properties, which sulfur compound is free frommetallic radicals, has not more than a single polar radical andpossesses a minimum of '7 carbonatoms.

2. An aviation lubricating oil containing from about 0.04% to 0.2 basedon sulfate ash, of an oil-miscible metal salt of the condensationproduct of a low molecular weight aldehyde and an aromatic hydroxycompound and from-about 0.05% to 0.2%, based on added sulfur, of anoil-soluble, organic, sulfur-containing antioxidant, substantially freefrom polar and 'metallic radicals and the the

6. The composition of claim 2 wherein the aro-- matic hydroxy compoundis an oil-soluble alkyl phenol.

the

7. The composition of claim'2 wherein the aromatic hydroxy compound isan alkyl naphthol.

8. The composition of claim 2 wherein the aromatic hydroxy compound isan octyl phenol.

9. The composition of claim 2 wherein the antioxidant is a sulfurizedwax olefin having a molecular weight of about 225 to 425.

10. The composition of claim 2 wherein the antioxidant is a, compound ofthe formula RSSR' wherein R and R are hydrocarbon radicals.

11. The composition ,of claim 2 which additionally contains a detergentquantity of calcium salt of oil-soluble petroleum sulfonic acid.

12. The composition of claim 1 wherein the oil is an aviationlubricating oil having a Sayboll Universal viscosity of about -125seconds at 210 F.

13. The composition of claim 1 which additionally contains anoil-soluble detergent.

14. The composition of claim 2 wherein the sulfur-containing antioxidantis a wax disulfide 15. An aviation mineral lubricating oil containingfrom about 0.04% to, 0.2%, based on sulfate ash, of anoil-solublecalcium salt of the condensation product of formaldehyde andan oil soluble alkyl phenol, and from about 0.025% tc 0.30%, based onadded sulfur, of an oil-soluble sulfur-containing, parafiln wax,oxidatior inhibitor.

' JOHN R. GRIFFIN, JR.

PAUL R. VAN ESS.

